Chapter 1
 Introduction to the Scientific Method
Can Science Cure the Common Cold?
The Process of Science
 Science is not a giant collection of facts to be memorized.
 Process, using the scientific method:
 Observing
 Proposing ideas
 Testing
 Discarding those ideas that fail
The Nature of Hypotheses
 Hypothesis: proposed explanation
 Testable and potentially falsifiable
 Where do hypotheses come from?
 Both logical and creative influences are used
Scientific Theory
 Powerful, broad explanation of a large set of observations
 Rests on many hypotheses that have been tested
 Generates additional hypotheses
The Logic of Hypothesis Tests
 Example: consuming vitamin C decreases the risk of catching a cold
 Inductive reasoning: combining a series of specific observations into a
generalization
 To test, make a prediction using deductive reasoning.
 Involves using general principle to predict an expected observation
 “if…then” statement
 A hypothesis that fails our test is rejected and considered disproven.
 A hypothesis that passes is supported, but not proven.
 Why not? An alternative hypothesis might be the real explanation.
 The most powerful way to test hypotheses: do experiments
The Experimental Method
 Experiments are contrived situations.
 Variables: factors that can change in value under different conditions
 Independent variables can be manipulated by the scientist
 Dependent variables cannot be changed by the researcher
Controlled Experiments
 Controlled experiment: tests the effect of a single variable
 Control: a subject who is not exposed to the experimental treatment
 Differences can be attributed to the experimental treatment.
 Example: Echinacea tea experiment:
 Hypothesis: drinking Echinacea tea relieves cold symptoms
 Experimental group drinks Echinacea tea 5-6 times daily.
 Control group drinks “sham” Echinacea tea (placebo).
 Both groups rated the effectiveness of their treatment on relieving cold
symptoms.
 People who received echinacea tea felt that it was 33% more effective at
reducing symptoms.
Minimizing Bias in Experimental Design
 If human subjects know whether they have received the real treatment or a
placebo, they may be biased.
 Blind experiment: subjects don’t know what kind of treatment they have
received
 Double blinding: the person administering the treatments also doesn’t know
until after the experiment is over
 “gold standard” for experimentation
Using Correlation to Test Hypotheses
 It is not always possible or ethical to experiment on humans.
 Using existing data, is there a correlation between variables?
 Hypothesis: stress makes people more susceptible to catching a cold
 Is there a correlation between stress and the number of colds people have
caught?
 Caution! Correlation does not imply causation.
 The correlation might be due to other reasons.
Overview: What Statistical Tests Can Tell Us
 We can extend the results from small samples to an entire population.
 Difference between two samples: real or due to chance?
The Problem of Sampling Error
 Sampling error: the effect of chance
 We can calculate the probability that a result is simply due to sampling error.
 Statistically significant: an observed difference is probably not due to
sampling error
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Confidence interval: the range of values from a sample that has a 95%
probability of containing the true population mean (average).
Much population variation = large confidence interval
Small population variation = small confidence interval
What Statistical Tests Cannot Tell Us
 If an experiment was designed and carried out properly
 Evaluate the probability of sampling error, not observer error
 May not be of any biological significance
Primary Sources
 Researchers can submit a paper about their results to a professional journal
(primary source).
 Peer review: evaluation of submitted papers by other experts
 Secondary sources: books, news reports, the internet, and advertisements
Information from Anecdotes
 Anecdotal evidence is based on one person’s experience, not on experimental
data.
 Example: a testimonial from a celebrity
Science in the News
 Secondary sources may be missing critical information or report the information
incorrectly.
 Consider the source of media reports.
 Be careful with the internet since anyone can post information.
 Be very cautious about claims made in paid advertisements.
Understanding Science from Secondary Sources
 Use your understanding of the process of science to evaluate science stories.
 News media generally highlight only those science stories that seem
newsworthy.
 They are more likely to report a positive result than a negative one.
Is There a Cure for the Common Cold?
 No, but prevention methods are known.
 Wash your hands!
 No effect on cold susceptibility:
 Vitamin C
 Exposure to cold temperatures
 Exercise
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No vaccine for the common cold